Due to a worldwide concern about reduction in greenhouse gas, the development for medium-sized heat supply technology for utilizing new renewable energy heat sources with low temperatures that are scattered on the periphery, without using fossil fuel has been requested. Since a greater part of thermal demand from the center of a big city or surroundings is less than 100° C., it is very inefficient to directly use high-temperature and high-quality energy generated by combustion of fossil fuel. However, due to limitations in transportation and storage technology of thermal energy, technology development for thermal energy has been delayed compared to other energy sources.
Korean Patent Publication No. 2011-0021501 discloses a combined air conditioning system and a dual heat source supply system using new renewable energy as a heat source. However, the above technique is just the usage of new renewable energy instead of existing fossil fuel and has limitations in considering a thermal energy network considering a distributed heat source or heat transportation efficiency.